1. Field of the Invention
The present invention relates to an air-pressure type excitation apparatus for actively suppressing vibration of a control-subject vehicle etc. by utilizing such excitation force of an actuator equipped with a closed air chamber as to be based on a pressure variation caused inside the air chamber by alternately switching a state of communication to the air chamber from two air-pressure sources having different air pressures owing to electromagnetic switching means such as an electromagnetic valve.
2. Description of the Related Art
Conventionally, this sort of air-pressure type excitation apparatus controls the switching operations of the switching valve by utilizing a drive control signal formed on the basis of a reference signal correlated with an oscillation frequency of a standard signal and an oscillation amplitude of a state signal sent from a vibration generation source. As this drive control signal, a pulse signal is used which has the same frequency as the oscillation frequency and also which is converted the oscillation amplitude into a duty ratio of the pulse corresponding to the oscillation frequency of the standard signal and the oscillation amplitude of the state signal.
To reduce the actuator""s excitation force, that is the vibration suppressing force by the excitation apparatus, using the drive control signal, adjustment is made to reduce the duty ratio of the pulse of the drive control signal. The excitation force, on the other hand, hits a maximum when the duty ratio of the pulse of the drive control signal is about 50-60%, so that as the pulse duty ratio goes away from the value of 50-60%, a harmonic component increases with respect to a control frequency of the drive control signal. As the harmonic component thus increases, the vibration of other than the control frequency and the corresponding noise increase on what is subject to vibration control such as a vehicle, thus deteriorating the vibration suppressing effects.
To guard against this, there is a method available for providing and utilizing a muffler such as a branch hose etc. somewhere along an air flow path between the air chamber and the switching valve to thereby attenuate an air pressure fluctuation in a frequency band outside the frequency of the vibration to be suppressed. By this control method, however, the control costs are high, so that it is difficult to provide an inexpensive excitation apparatus. There is another method available for providing an excitation apparatus with filter characteristics relating to the excitation force thereof to thereby limit the frequency of its effective excitation force down to a predetermined value or less, thus removing a useless harmonic component. This method, however, narrows the band of the operating frequency of the excitation apparatus, so that its applications are limited, which is a problem.
In view of the above, it is an object of the present invention to provide an air-pressure type excitation apparatus which can remove a harmonic component inexpensively with a simple configuration and also which can give proper excitation force.
To achieve this object, a first aspect of the present invention comprises an actuator equipped with a closed air chamber, electromagnetic switching means which is provided somewhere along an air flow path connected to the air chamber and also which alternately switches a state of communication to the air chamber from two air pressure sources having different air pressures, and drive control signal generation means which generates a drive control signal based on a reference signal correlated with an oscillation frequency of a standard signal and an oscillation amplitude of a state signal sent from a vibration generation source, in such a configuration that the drive control signal is used to control switching operations of the electromagnetic switching means to thereby give birth to a pressure variation inside the air chamber in order to actively suppress control-subject vibration utilizing such excitation force of the actuator as to be based on the pressure variation, in which the drive control signal is pulse-width modulated corresponding to an amplitude of the reference signal, includes at least one pulse for each period of the reference signal, and is synchronized with the standard signal.
In the first aspect, the drive control signal is pulse-width modulated corresponding to the amplitude of the reference signal and also includes at least one pulse for each period of the standard signal. The drive control signal, therefore, can be composed of the pulses having a duty ratio of about 50-60%. As a result, it is possible to suppress a harmonic component with respect to the control frequency, which gives rise to a problem as the pulse duty ratio goes away from the value of 50-60%. Furthermore, since the drive control signal is synchronized with the standard signal, it is possible to prevent fluctuations of a low frequency, which occur when the waveform of the drive control signal changes if it is not synchronized instead. It is thus possible to suppress the vibration of other than the control frequency and the corresponding noise on a vehicle, thus easily and properly obtaining the vibration suppressing effects of the air-pressure type excitation apparatus.
A second aspect of the present invention comprises an actuator equipped with a closed air chamber, electromagnetic switching means which is provided somewhere along an air flow path connected to the air chamber and also which alternately switches a state of communication to the air chamber from two air pressure sources having different air pressures, drive control signal data storage means which stores data of a plurality of drive control signals generated beforehand by drive control signal generation means based on a reference signal correlated with an oscillation frequency of the standard signals and an oscillation amplitude of the state signals with regard to a plurality of different standard signals and state signals are sent from a vibration generation source, and drive control signal output means which reads out the drive control signal data from the drive control signal data storage means corresponding to the oscillation frequency of the standard signal and the oscillation amplitude of the state signal when the signals are received, to then output the drive control signal, in such a configuration that the drive control signal is used to control switching operations of the electromagnetic switching means to thereby give birth to a pressure variation inside the air chamber in order to actively suppress control-subject vibration utilizing such excitation force of the actuator as to be based on the pressure variation, in which the drive control signal is pulse-width modulated corresponding to an amplitude of the reference signal, includes at least one pulse for each period of the reference signal, and is synchronized with the standard signal.
In the second aspect, besides the actions of the above-mentioned first aspect, when having received the standard signal and the state signal, the drive control signal output means reads out a drive control signal corresponding to the oscillation frequency of this standard signal and the oscillation amplitude of this state signal from the drive control signal data storage means and then outputs this drive control signal. The drive control signal, therefore, can be generated easily and inexpensively. Moreover, in the drive control signal, a harmonic component can be easily suppressed with respect to a control frequency. Furthermore, it is possible to easily prevent fluctuations in the low frequency, which occur when the waveform of the drive control signal changes. This results in a simple configuration of the control section of the air-pressure type excitation apparatus, thus reducing the costs of the control-related parts greatly.
Besides, according to the present invention, the reference signal may be a sine wave signal given on the basis of an oscillation frequency of the standard signal and an oscillation amplitude of the state signal. It is, therefore, possible to easily generate the drive control signal by performing pulse width modulation on the reference signal, which is thus given as a sine wave signal.
Furthermore, according to the present invention, the number of pulses of the drive control signal for each period of the reference signal can be changed corresponding to the control frequency of the standard signal so that the product of the number of the pulses and the control frequency not larger than a responding frequency of the electromagnetic switching means. By thus changing the number of pulses of the drive control signal for each period of the reference signal corresponding to the control frequency of the standard signal, the drive control signal can be composed of the proper pulses that match a range of the control frequency. Furthermore, by thus limiting the product of the number of the pulses and the control frequency down to the responding frequency of the electromagnetic switching means or less, the electromagnetic switching means can be driven properly by the drive control signal.